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DESCRIPTION

[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
the ISO C standard.

The isalnum() function shall test whether c is a character of class alpha or digit in the program's
current locale; see the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 7,
Locale.

The c argument is an int, the value of which the application shall ensure is representable as an unsigned
char or equal to the value of the macro EOF. If the argument has any other value, the behavior is undefined.